As is well known, thinning of glass sheets to be used in flat panel displays (FPD), such as a liquid crystal display, a plasma display, and an OLED display, glass sheets to be used in OLED illumination, glass sheets to be used for producing a tempered glass that is a component of a touch panel, and the like, and glass sheets to be used in panels of solar cells, and the like has been promoted in the current circumstances.
For example, in Patent Literature 1, there is disclosed a glass film (thin sheet glass) having a thickness of several hundred micrometers or less. As described also in this literature, this kind of glass film is generally obtained through continuous forming with a forming device employing a so-called overflow down-draw method.
For example, an elongated glass film obtained by the continuous forming by the overflow down-draw method is changed in its conveying direction from a vertical direction to a horizontal direction, and is then continuously conveyed to a downstream side with a lateral conveying unit (horizontal conveying unit) of a conveying device. In the process of the conveyance, both end portions (selvage portions) of the glass film in a width direction are cut and removed. After that, the glass film is taken up into a roll shape with a take-up roller. Thus, a glass roll is formed.
In Patent Literature 1, as a method of cutting both the end portions of the glass film in the width direction, laser cleaving is disclosed. The laser cleaving involves forming an initial crack on the glass film by crack forming means, such as a diamond cutter, and then irradiating the portion with a laser beam to heat the portion, followed by cooling the heated portion by cooling means to develop the initial crack through a thermal stress generated in the glass film, to thereby cut the glass film.
As another cutting method, there is used laser melt-cutting involving radiating a laser beam to a glass film to melt-cut part of the glass film. As illustrated in FIG. 10A and FIG. 11, in the laser melt-cutting, while a glass film G is conveyed in a predetermined direction (in the direction represented by the symbol “X” in FIG. 11) with a conveying device 101, a laser beam LB is radiated to a predetermined position (irradiation position) O of the glass film G from a laser irradiation apparatus 102.
The conveying device 101 includes a first conveying body 101a and a second conveying body 101b arranged so as to be spaced apart from each other. The irradiation position O with the laser beam LB is set between the first conveying body 101a and the second conveying body 101b. An assist gas AG is blown toward the glass film G so that molten glass is prevented from scattering and remaining as dross.
As illustrated in FIG. 10B, through irradiation with the laser beam LB, the glass film G is melt-cut into a first portion G1 and a second portion G2. Molten glass G3 generated through the melt-cutting falls into a space between the first conveying body 101a and the second conveying body 101b, and collected at a bottom of the space.